1. Field of the Invention
The present invention relates to a sewing machine which has a bobbin thread cutting blade in a throat plate, installs a bobbin thread bobbin in a sewing machine bed during a sewing preparation stage and draws out the bobbin thread onto the throat plate and cuts the thread to an appropriate length, and maintains the bobbin thread in a tense state generated when the bobbin thread is cut, so that the bobbin thread and the needle thread are appropriately interlocked with certainty.
2. Description of the Related Art
In the sewing operation using a household sewing machine, a needle thread and a bobbin thread are set in a sewing preparation step. The setting process is performed as follows. First a bobbin is installed in an inner rotary hook of a horizontal rotary hook. Then the bobbin thread is drawn out onto a throat plate while hooking the bobbin to a tension applying device of the inner rotary hook.
At this time the bobbin thread is drawn out with some slack from a tension generation portion onto the throat plate. The thread drawn out of the throat plate is cut to an appropriate length. When the sewing machine starts, the horizontal rotary hook operates, thereby the bobbin thread is caught and the bobbin thread and the needle thread appropriately interlock. Setting then completes.
The portion of the bobbin thread drawn out of the throat plate is cut to an appropriate length by a cutting blade of a cutting device attached to a part of the throat plate. There are various sewing machines having such a cutting device included in the throat plate, and these are disclosed in Japanese Patent Application Laid-open No. H4-96790, Japanese Patent Application Laid-open No. H4-96791 and Japanese Patent Application Laid-open No. 2002-336579.
Japanese Patent Application Laid-open No. H4-96790, Japanese Patent Application Laid-open No. H4-96791 and Japanese Patent Application Laid-open No. 2002-336579 disclose a sewing machine provided with a cover member disposed on a concave portion formed on a top face of a bed portion of the sewing machine, a holding space that is formed between the bottom face of the cover member and the concave portion, a cutting blade disposed in the bed portion, and a guide groove that is connected with the holding space in the bed portion and extends continuously on the top face of the bed portion from a housing opening to the cutting blade, so as to guide a bobbin thread drawn out of the housing opening to the cutting blade, wherein the holding space holds the bobbin thread which passed through the guide groove so that the bobbin thread does not upward.
This configuration allows the bobbin thread which is drawn out onto the throat plate to be cut to an appropriate length very easily, and the bobbin thread can be efficiently set by a device constituted by the horizontal rotary hook (the outer rotary hook and the inner rotary hook) and the bobbin.